Eicosapentaenoic Acid Plays a Beneficial Role in Membrane Organization and Cell Division of a Cold-Adapted Bacterium, Shewanella livingstonensis Ac10
Eicosapentaenoic Acid Plays a Beneficial Role in Membrane Organization and Cell Division of a Cold-Adapted Bacterium, Shewanella livingstonensis Ac10
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DOI：
10.1128/jb.00881-08
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发表时间：
2009-01-15
影响因子：
3.2
通讯作者：
Esaki, Nobuyoshi
中科院分区：
文献类型：
--
作者：
Kawamoto, Jun;Kurihara, Tatsuo;Esaki, Nobuyoshi
利文斯通希瓦氏杆菌Ac10是从南极海水中分离到的一种耐冷性革兰氏阴性细菌，它在低温下产生二十碳五烯酸(EPA)作为磷脂的一种成分。EPA约占4℃下生长的细胞总脂肪酸的5%。我们发现，有五个基因，称为ORF2，orf5，orf6，orf7和orf8，通过靶向干扰各自的基因来合成EPA。缺乏EPA的突变体在4℃时表现出明显的生长迟缓，但在18℃时不表现出明显的生长迟缓。补充在sn-2位含有EPA的合成磷脂酰乙醇胺补充了生长缺陷。不含EPA的突变体呈丝状，在4℃时在单个细胞内观察到多个类核，表明该突变体在细胞分裂方面存在缺陷。对细胞进行高压冷冻和冷冻置换后的电子显微镜观察发现，在4℃时，EPA缺失突变体的细胞膜存在异常。我们还发现，几种膜蛋白的含量受到EPA耗竭的影响。虽然多不饱和脂肪酸通常被认为增加了疏水膜核心的流动性，但在EPA缺失的突变体和亲本菌株中，由脂类提取物制备的大单层囊泡和细胞膜中疏水的小分子芘的扩散非常相似。这些结果表明，Livingstonsis Ac10中的EPA不是大分子双层流动性所必需的，但在低温下对膜组织和细胞分裂起到有益的作用，可能是通过EPA与参与这些细胞过程的蛋白质之间的特异性相互作用。
Shewanella livingstonensis Ac10, a psychrotrophic gram-negative bacterium isolated from Antarctic seawater, produces eicosapentaenoic acid (EPA) as a component of phospholipids at low temperatures. EPA constitutes about 5% of the total fatty acids of cells grown at 4 degrees C. We found that five genes, termed orf2, orf5, orf6, orf7, and orf8, are specifically required for the synthesis of EPA by targeted disruption of the respective genes. The mutants lacking EPA showed significant growth retardation at 4 degrees C but not at 18 degrees C. Supplementation of a synthetic phosphatidylethanolamine that contained EPA at the sn-2 position complemented the growth defect. The EPA-less mutant became filamentous, and multiple nucleoids were observed in a single cell at 4 degrees C, indicating that the mutant has a defect in cell division. Electron microscopy of the cells by high-pressure freezing and freeze-substitution revealed abnormal intracellular membranes in the EPA-less mutant at 4 degrees C. We also found that the amounts of several membrane proteins were affected by the depletion of EPA. While polyunsaturated fatty acids are often considered to increase the fluidity of the hydrophobic membrane core, diffusion of a small hydrophobic molecule, pyrene, in the cell membranes and large unilamellar vesicles prepared from the lipid extracts was very similar between the EPA-less mutant and the parental strain. These results suggest that EPA in S. livingstonensis Ac10 is not required for bulk bilayer fluidity but plays a beneficial role in membrane organization and cell division at low temperatures, possibly through specific interaction between EPA and proteins involved in these cellular processes.